looks like they need water if you know they don't then they are root bound which can be caused by a number of things.
I think your spot on about the nitrogen tox I thought it may be ph so I flushed it an stuff soil ph is between 6.5 and 7.0 at the min white there drying out from flushing I seen some pix online that looked just like my plants that was suffering from nitrogen tox I'm going to research ways to rectify nitro tox see if I can sort it oh yeah zubey temps are about 28 average don't think that's the problem broClawing is do to nitrogen toxien, you don't have clawing, more look like over watering to me (=not to much water, but to little time in between waterings, not allowing the medium to dry out a bit and that way lock out oxygen from the root zone)
if you think that might be the case look at this link:
http://hubpages.com/hub/Hydrogen-Peroxide-for-Plants
I have saved my plant`s before with 5ml of 3% H2O2 in a gallon of water, helps drying out the medium quicker, wile it deliver oxygen to the root zone and also remove any root rot if they got any
BUT, I base this on the pictures and info you provided, so like with every other advice in here take it with a grain of salt so to speak, and do your own research as well, and try to come to the most logical conclusion, under watering could look similar
My plant is looking similar to yours Messi. I'm a first time grower and also looking for advice here. I did a quick check of my SOIL pH by mixing a small amount of it in distilled water and found it to be 5.4 pH. I've been regularly watering the plant with 6.4-6.6 water but probably watered too often in the past week. I'm hoping it's an "overwatering" issue and I can just wait it out until the medium (50% promix and 50% perlite) dries out. I'll then start spacing water out to allow for medium oxygen. I have worked about half a teaspoon of lime into the top of the medium to help bring up the soil pH a bit. This is an AK47 auto in it's 47th day.
If you have dark green fan leaves and you are still feeding the plant, you have too much N. If your fan leaves are losing their gloss and starting to fade, you have too little. Simple as that in my world.Ps how do I know if it's to much nitro or to little?